This invention relates to an optical recording system, and in particular, to a recording system which uses an optical recording disk and optical head to record, reproduce and erase data.
FIG. 9 illustrates a conventional optical recording system, generally indicated as 900, for reading and recording a magneto optical disk 901. For recording, a laser diode 906 is provided as a light source and outputs a light beam 911 which is collimated by a collimater 905. The collimated beam passes through a one-way mirror 903 to a second mirror 912 which directs the light beam through an objective lens 902 which focuses the light upon magneto optical disk 901.
For reading magneto optical disk 901, light is reflected back through objective lens 902 and reflected by mirror 912 towards one-way mirror 903. Light returning in the opposite direction as light beam 911 through one-way mirror 903 is directed away from laser diode 906 towards a wave plate 907. The light then passes through wave plate 907 and a lens 909 to a polarized beam splitter 908 which splits the beam. Polarized beam splitter 908 divides the beams. A portion of the beam is received by each respective photo diode 910. The signals from photo diodes 910 are then converted to a machine interpretable form and compared with each other.
The prior art recording system has been satisfactory. However, it suffers from the disadvantage that it provides a slow recording media access time and data transfer rate.
An optical recording head constructed as a floating head such as that used in hard disk drives was recently presented at an academy by Mr. Ukita of Nippon Telephone and Telegram and was published in Japanese application No. 41509/87. This optical head was a floating head similar to those used in a hard disk drive, but was made light weight to improve access speed approaching limits only available with hard disks. This device was also satisfactory. However, the device was not adaptable to a magneto optical disk. Additionally, this recording system can not perform over writing.
Several studies were conducted and published concerning improvements of these conventional optical heads. A study of a thin film optical head was presented in an abstract of the spring lecture meeting of the Japan Applied Physics Association 28p-Ze-13, 1987. A study of a slider optical head which was similar to a magnetic head for hard disk drives was presented in Trans. IEICE, E71, p. 323, 1988. These studies were directed to improving access speed by decreasing head weight.
A further study showed that a data transfer rate could be improved by combining an optical head and a magnetic head and was made public in an abstract of the spring lecture meeting of the Japan Applied Physics Association 21a-Zq-7.
Magneto optical media was studied and the results were made public in an abstract of the Japan Applied Physics Association 28p-ZL-3. In this study, a magneto optical media can be overwritten by using a two layered thin recording film. An improvement for a recording medium which may be overwritten using phase change material was demonstrated in the Japan Optical Memory Symposium 1988, p. 81.
These conventional techniques were satisfactory. However, they suffer from several disadvantages. First, a recording system using a thin film optical head or slider head is not able to produce information on magneto optical media. A magneto optical medium using two layered recording film results in a high manufacturing cost and requires a strong magnet to initially record on the film. Lastly, an overwriting phase change medium suffers from weak stability.
Accordingly, it is desirable to provide a recording system which overcomes the disadvantages of the prior art and provides an advanced recording system having high access speed, high speed data transfer, is capable of reproducing magneto optical data and is capable of overwriting previously recorded data.